Field of the Invention
The present invention relates to a pneumatic tire having a belt layer which is buried in a tread portion, and a belt reinforcing layer which is arranged in an outer side in a tire diametrical direction of the belt layer.
Description of the Related Art
Conventionally, in a pneumatic tire, for the purpose of improving a high-speed durability and improving a steering stability, one or more belt reinforcing layers are provided between the tread rubber and the belt layer.
In the following patent document 1, there is described a pneumatic tire in which belt reinforcing layers constructed by an organic fiber are provided in an outer side of a belt layer, and a driving number of the belt reinforcing layers is reduced little by little from a bent end toward a center side, for the purpose of improving the high-speed durability without deteriorating a smooth handling property at the cornering.
A tire ground pressure distribution when a vehicle turns is the highest at a shoulder portion of a vehicle installation outer side (hereinafter, also referred to as an out side) of a tire positioned in an outer side (hereinafter, referred to an outer wheel), and is next higher at a shoulder portion of a vehicle installation inner side (hereinafter, also referred to as an in side) of a tire positioned in an inner side (hereinafter, referred to an inner wheel). As a result, if the belt reinforcing layers are arranged in symmetrical to a tire equator such as the pneumatic tire of the patent document 1, there is a risk that the reinforcement is insufficient at the out side of the outer wheel and a sufficient cornering power cannot be obtained when a vehicle turns, or there is a risk that the reinforcement becomes excessive at the in side of the inner wheel and a weight is increased. On the other hand, if the belt reinforcing layers are arranged in asymmetrical to the tire equator, expansion coefficient is different between right and left and a conicity may be increased.
Further, in the following patent document 2, there is described a pneumatic tire provided with asymmetric patterns which are differentiated in tread patterns between both sides of a tire equator in a tread portion, wherein the pneumatic tire is differentiated in a cord arrangement density of the belt reinforcing layer between right and left of the tire equator. As a result, increase of the conicity in the tire having the asymmetric pattern is suppressed without causing any weight increase.
However, the invention according to the patent document 2 is the pneumatic tire having the asymmetric pattern, and if the cord arrangement density of the belt reinforcing layer is differentiated between right and left of the tire equator in the tire having the symmetric pattern, the expansion coefficients are different between right and left, and the conicity is increased.